The sultry "Really Love" is a smooth gateway to
Black Messiah
, D'Angelo's first album in 15 years. Opening with a swell of strings and a flamenco guitar, not to mention a sexy female voice whispering in Spanish, the boudoir ballad reaches a slow sizzle by the time D'Angelo's falsetto beckons his lady to let "our nectars mingle." The soulful track, which samples
Curtis Mayfield
's "We the People Who Are Darker Than Blue," peaked at No. 43 on the Hot R&B/Hip-Hop Songs chart, while the album bowed at No. 5 on the Billboard 200. "Really Love" is the outlier of the category -- a layered ode to devotion from an otherwise politically charged album, and a nomination that few Grammy prognosticators saw coming.

The most unapologetically exuberant song since
Pharrell Williams
' "Happy," "Uptown Funk!" spent 14 weeks at No. 1 on the Billboard Hot 100, while the video topped 1 billion global views. This ode to the horn-filled R&B of the '70s started as a jam in Mars' studio, with the now-instantly recognizable
Chic
-like opening guitar line not coming until the very end. Ronson told NPR he stressed so much over his guitar part that he fainted in a restaurant. "When you're doing something that doesn't sound like anything else on the radio at the time," he said, "you almost need to, like, iron-clad it to make sure it gets through."

On this paean to eternal love -- or at least a love that lasts until he's 70 -- Sheeran turned to frequent collaborator Jake Gosling, with whom he worked on his label debut,
+
, to produce the earnest guitar- and keyboard-based track. It has paid off: The ballad became the first song to spend a full year in the Official U.K. Singles Chart top 40, grabbing 500 million Spotify streams and reaching No. 2 on the Hot 100. But perhaps most of all, it became an instant classic at weddings and anniversary parties, in no small part due to the romantic video, which features Sheeran learning how to ballroom dance.

To complete her move from country to pop, Swift returned to Swedish hook master (and 2015 Grammy producer of the year) Max Martin, who co-produced nine songs on
1989
, including this No. 1 nugget. Built on an infectious programmed drum loop, some of her cleverest and most biting lyrics and a cascading bridge, Swift distills the entirety of an up-and-down relationship into a neatly packaged four minutes. The song's video became the most-viewed in Vevo's history in October, and that wasn't all: When "Blank Space" leapt 13-1 on the Hot 100 in November, Swift became the first solo woman in the history of the chart to replace herself in the peak position.

One of two songs in this category to feature the work of 2015 Grammy producer of the year Max Martin, The Weeknd's "Can't Feel My Face" spent three nonconsecutive weeks at the top on its way to ubiquity. The song's driving, upbeat rhythm contrasts with its tortured lyrics as The Weeknd compares his lover to a drug, predicting that "she'll be the death of me." Most significantly, the sleek,
Michael Jackson
-channeling dance-pop tune resided at the top while The Weeknd's "The Hills" climbed to No. 2, making the Canadian crooner the first lead artist to simultaneously have the top two songs since 2009, the highlight of a truly breakout year.